www.cardiologyjournal.org 281 CASE REPORT
Cardiology Journal 2008, Vol. 15, No. 3, pp. 281–283 Copyright © 2008 Via Medica ISSN 1897–5593
Address for correspondence: Konstantinos G. Kouvelas, MD, Hellenic Red Cross General Hospital, Erythrou Stavrou 1
& Athanasaki str., 11526 Athens, Greece, tel: +30 210-6414 705, 210-8104 554, fax: +30 210-641 4587, e-mail: drkokouv@gmail.com
Received: 24.01.2008 Accepted: 16.03.2008
Irregular ventricular tachycardia underdetected by implantable cardioverter defibrillator device
Athanasios G. Manolis, Spyros Kourouklis, Dimitrios Chatzis, Konstantinos Kouvelas and Zenon Kyriakides
2nd Department of Cardiology. Hellenic Red Cross General Hospital, Athens, Greece
Abstract
A case of sustained monomorphic ventricular tachycardia underdetected by a single chamber implantable cardioverter defibrillator because of RR interval irregularity is presented. The programmed stability criterion is responsible for the underdetection. Special attention must be paid when it comes to programming this detection parameter. (Cardiol J 2008; 15: 281–283) Key words: irregular ventricular tachycardia, implantable cardioverter defibrillator, amiodarone
Case report
Ischemic heart failure has been associated with the increased risk of lethal ventricular tachyarrhy- thmias. Implantable cardioverter defibrillator (ICD) is an established treatment, for the primary and/or the secondary prevention of sudden arrhythmic death in these patients. In ICD detection algori- thms, the stability criterion of consecutive RR in- tervals should be programmed very carefully for the prevention of inappropriately delivered therapies by the device, especially in patients with concomitant supraventricular irregular tachyarrhythmias.
We present a patient with ischemic heart fa- ilure, left bundle branch block in the basal surface ECG and known paroxysmal atrial fibrillation un- der amiodarone therapy. A single chamber ICD device (Biotronik, Belos VR) was implanted for secondary prevention after an episode of hemody- namically unstable sustained monomorphic ventri- cular tachycardia (SMVT). The device has been programmed for a three-zone therapy, slow ventri- cular tachycardia (VT) (130 to 171 bpm), fast VT (171 to 214 bpm) with the stability interval set at
± 20 ms and ventricular fibrillation (VF). The co- unter of detection was set at 26 and at 16 RR inte- rvals in the slow and fast VT zone, respectively.
In the slow VT zone, the programmed therapy consisted of 2 antitachycardia pacing schemes (burst type with 6 consecutive pulses) each containing 3 sequences, followed by cardioversion. In the fast VT zone, the programmed therapy consisted of cardiover- sion sequences (the first attempt was set at 7 J).
In the VF zone, the programmed therapy consisted of defibrillation shocks (the first shock was set at 20 J, and the remaining shocks were set at 30 J).
During a 24 hours ambulatory ECG recording, an episode of SMVT (Fig. 1) occurred at a mean initial rate of 150 bpm, with unstable RR intervals (Fig. 2A, B). The ICD device was unable to detect this irregular rhythm in the slow VT zone. After- wards, this ventricular rhythm was accelerated to a faster but regular SMVT (180 bpm) (Fig. 2C), which was detected in the fast VT zone. The pro- grammed cardioversion therapy of 7 J was followed by degeneration of the fast VT to VF and the sinus rhythm was finally restored after two consecutive shocks of 20 J and 30 J, respectively (Fig. 1).
In order to eliminate underdetected irregular VT episode in the future, the stability interval was reprogrammed to ± 40 ms, based on the calculated mean values of the RR intervals differences during the recorded tachycardia.
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Figure 1. A 24 hours ambulatory ECG recording (dual channel) in an ICD recipient, showing an undetected episode of irregular ventricular tachycardia, lasting about 1.5 min. This rhythm was then accelerated to a faster but regular ventricular tachycardia followed by cardioversion, which led to the degeneration of ventricular tachycardia to ventricular fibrillation. Finally, the sinus rhythm was restored after two consecutive delivered shocks of 20 J and 30 J, respectively.
Figure 2. A. Initiation of a slow ventricular tachycardia; B. Ongoing slow ventricular tachycardia with irregular cycle length intervals; C. Acceleration of the slow and irregular ventricular tachycardia to a faster but regular cycle length interval form.
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B
C
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283 Athanasios G. Manolis et al., Irregular ventricular tachycardia, ICD underdetection
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Discussion
The cycle length of SMVT is usually stable.
Stabilization of the cycle length occurs after 10 to 20 beats from the initiation of the arrhythmia [1]. In addition, irregularity in the cycle length during on- going VT has been observed in 20% of episodes [2].
In ICD devices, a programmed stability inte- rval of 50–60 ms combined with a number of 12 to 16 RR intervals has the ability of a proper detec- tion over 90% of irregular VT episodes [3]. The probability of RR intervals irregularity increases in slower VT as well as in patients under antiarrhyth- mic therapy [4–6]. The underlying mechanism of cycle length irregularity is not well understood.
Rate dependent changes in the electrophysiologic properties of the arrhythmogenic substrate (con- duction velocity, refractory period) may contribute to the prescribed irregularity.
Given that the aforementioned underdetection was due to the programmed stability criterion, spe- cial attention must be paid when it comes to pro- gramming this detection parameter.
Acknowledgements
The authors do not report any conflict of inte- rest regarding this work.
References
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